The mechanisms of protein localization are of central biological importance at all levels, from the functioning of individual molecules to the biogenesis of higher ordered structures, including the cell itself. Although secreted proteins have a general requirement for some type of cellular export mechinery, the details of such secretion systems are not known. The overall objective of this work is to use E. coli as a model system to determine the composition, function, and number of such cellular secretion systems. Initial work is aimed at using a combination of genetics and biochemistry to define one secretion system, the secA system. Genetic approaches will be used to define the genes which code for the components of this system and to obtain mutants in these genes. The secreted proteins which use this system will be identified using currently available mutants (SecA-) in the export system. The site on the polypeptide chain of the secreted protein which targets it to use this expert system will be determined using gene fusion technology to create specific hybrid proteins of interest. This latter study is aimed at understanding the specific interactions of secreted proteins with individual components of the export machinery. This should allow a structure-function analysis for this secretion system.